Constraints https://doi.org/10.1007/s10601-019-09307-9 XCSP 3 and its ecosystem Gilles Audemard 1 · Fr´ ed´ eric Boussemart 1 · Christophe Lecoutre 1 · C´ edric Piette 1 · Olivier Roussel 1 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract In this paper, we present a summary of XCSP 3 , together with its ecosystem. XCSP 3 is a format used to build integrated representations of combinatorial constrained problems. Interestingly, XCSP 3 preserves the structure of models, by handling arrays of variables and groups/blocks of constraints, which makes it rather unique in the literature. Furthermore, the ecosystem of XCSP 3 is well supplied: it includes companion tools (parsers and checkers), a website with a search engine for selecting and downloading instances, and competitions of solvers. The Java-based modeling API, called JvCSP 3 , is the last developed piece of this complete production chain. Keywords Format · Modeling 1 Introduction In this paper, we present XCSP 3 and its ecosystem. XCSP 3 is a major extension of the basic format XCSP 2.1 [42] that was introduced in 2009. XCSP 3 is a format that allows us to build integrated representations of combinatorial constrained problems. Actually, XCSP 3 can be seen as an intermediate Constraint Programming format preserving the structure of models. In other words, XCSP 3 is neither a flat format, such as XCSP 2.1 [42] or FlatZinc [2], nor a modeling language such as MiniZinc [36] or ESSENCE [17]. This is shown graphically in Fig. 1, and discussed throughout this paper. While modeling languages provide facilities  Gilles Audemard audemard@cril.fr Fr´ ed´ eric Boussemart boussemart@cril.fr Christophe Lecoutre lecoutre@cril.fr C´ edric Piette piette@cril.fr Olivier Roussel roussel@cril.fr 1 CRIL-CNRS, UMR 8188, University of Artois, Lens, France